docs: def substitution_rate(Nref, Nsubstitutions, eps=numpy.spacing(1)):
      """Substitution rate
  
      Parameters
      ----------
      Nref : int >=0
          Number of entries in the reference.
  
      Nsubstitutions : int >=0
          Number of substitutions.
  
      eps : float
          eps.
          Default value numpy.spacing(1)
  
      Returns
      -------
      substitution_rate: float
          Substitution rate
  
      """
  
      return float(Nsubstitutions / (Nref + eps))